The present invention relates to a process for the preparation of organosilicon disulfide compounds. Organosilicon disulfides are known adhesion promoters in sulfur-vulcanizable rubber mixtures reinforced with inorganic materials such as glass SiO2, aluminosilicates and carbon black. For example, in GB 1,484,909, there is disclosed a process for the preparation of organo trialkoxysilane disulfides. In accordance with the teachings of this reference, mercaptopropyl trimethoxy silane or mercaptopropyl triethoxy silane is reacted with sulfuryl chloride in an inert solvent at temperatures of from 0.degree. to 100.degree.. The disulfide is then obtained by fractional distillation. The yields of desired product range in the neighborhood of 63 to 65 percent of theoretical.
U.S. Pat. No. 3,842,111 discloses a method for the preparation of organosilicon disulfide compounds by oxidizing mercaptoalkoxysilanes. Representative oxidizing agents include oxygen, chlorine, halogens of atomic weight 35 to 127, nitric oxide, sulfuryl chloride and sulfoxides.
U.S. Pat. No. 5,675,014 relates to a process for the preparation of organosilicon disulfide compounds by reacting a mercaptoalkoxysilane with a dithiobis (benzothiazole) compound. Unfortunately, this process does not produce high purity bis organosilicon disulfide compounds due to the formation of unsymmetrical organosilicon disulfides.
U.S. Pat. No. 5,663,358 relates to a process for the preparation of organosilicon disulfide compounds by reacting a mercaptoalkoxysilane with a sulfenamide compound. Unfortunately, due to the formation of unsymmetrical organosilicon compounds, the purity of bis organosilicon disulfide compounds are reduced.
Generally speaking, bis organosilicon disulfide compounds are very expensive and, with the increasing interest in silica-reinforced vulcanizable rubber, more cost-efficient methods of preparing these compounds are needed.